亀川筋湯 (Kamegawa Sujiyu)

This is the tiniest onsen I have ever been to. They don't have running water and there is hardly any space to sit next to the bath.

The building looks like a shed.

It is not allowed to use shampoo here, but it seems you can use soap. Be careful not to let any soap get into the bath. As I had already washed myself after the sand bath, I just soaked for a few minutes and got out.